package p2p

import (
	"net"
	"runtime"

	"github.com/libp2p/go-libp2p-core/control"
	"github.com/libp2p/go-libp2p-core/network"
	"github.com/libp2p/go-libp2p-core/peer"
	"github.com/multiformats/go-multiaddr"
	manet "github.com/multiformats/go-multiaddr/net"
	"github.com/sirupsen/logrus"
)

const (
	// Limit for rate limiter when processing new inbound dials.
	ipLimit = 4

	// Burst limit for inbound dials.
	ipBurst = 8

	// High watermark buffer signifies the buffer till which
	// we will handle inbound requests.
	highWatermarkBuffer = 10
)

// InterceptPeerDial tests whether we're permitted to Dial the specified peer.
func (s *Service) InterceptPeerDial(_ peer.ID) (allow bool) {
	return true
}

// InterceptAddrDial tests whether we're permitted to dial the specified
// multiaddr for the given peer.
func (s *Service) InterceptAddrDial(pid peer.ID, m multiaddr.Multiaddr) (allow bool) {
	// Disallow bad peers from dialing in.
	if s.peers.IsBad(pid) {
		return false
	}
	return filterConnections(s.addrFilter, m)
}

// InterceptAccept checks whether the incidental inbound connection is allowed.
func (s *Service) InterceptAccept(n network.ConnMultiaddrs) (allow bool) {
	if !s.validateDial(n.RemoteMultiaddr()) {
		// Allow other go-routines to run in the event
		// we receive a large amount of junk connections.
		runtime.Gosched()
		log.WithFields(logrus.Fields{"peer": n.RemoteMultiaddr(),
			"reason": "exceeded dial limit"}).Trace("Not accepting inbound dial from ip address")
		return false
	}
	if s.isPeerAtLimit(true /* inbound */) {
		log.WithFields(logrus.Fields{"peer": n.RemoteMultiaddr(),
			"reason": "at peer limit"}).Trace("Not accepting inbound dial")
		return false
	}
	return filterConnections(s.addrFilter, n.RemoteMultiaddr())
}

// InterceptSecured tests whether a given connection, now authenticated,
// is allowed.
func (s *Service) InterceptSecured(_ network.Direction, _ peer.ID, _ network.ConnMultiaddrs) (allow bool) {
	return true
}

// InterceptUpgraded tests whether a fully capable connection is allowed.
func (s *Service) InterceptUpgraded(_ network.Conn) (allow bool, reason control.DisconnectReason) {
	return true, 0
}

func (s *Service) validateDial(addr multiaddr.Multiaddr) bool {
	ip, err := manet.ToIP(addr)
	if err != nil {
		return false
	}
	remaining := s.ipLimiter.Remaining(ip.String())
	if remaining <= 0 {
		return false
	}
	s.ipLimiter.Add(ip.String(), 1)
	return !s.peers.IsAboveInboundLimit()
}

// configureFilter looks at the provided allow lists and
// deny lists to appropriately create a filter.
func configureFilter(cfg *Config) (*multiaddr.Filters, error) {
	addrFilter := multiaddr.NewFilters()
	// Configure from provided allow list in the config.
	if cfg.AllowListCIDR != "" {
		_, ipnet, err := net.ParseCIDR(cfg.AllowListCIDR)
		if err != nil {
			return nil, err
		}
		addrFilter.AddFilter(*ipnet, multiaddr.ActionAccept)
	}
	// Configure from provided deny list in the config.
	if len(cfg.DenyListCIDR) > 0 {
		for _, cidr := range cfg.DenyListCIDR {
			_, ipnet, err := net.ParseCIDR(cidr)
			if err != nil {
				return nil, err
			}
			addrFilter.AddFilter(*ipnet, multiaddr.ActionDeny)
		}
	}
	return addrFilter, nil
}

// filterConnections checks the appropriate ip subnets from our
// filter and decides what to do with them. By default libp2p
// accepts all incoming dials, so if we have an allow list
// we will reject all inbound dials except for those in the
// appropriate ip subnets.
func filterConnections(f *multiaddr.Filters, a multiaddr.Multiaddr) bool {
	acceptedNets := f.FiltersForAction(multiaddr.ActionAccept)
	restrictConns := len(acceptedNets) != 0

	// If we have an allow list added in, we by default reject all
	// connection attempts except for those coming in from the
	// appropriate ip subnets.
	if restrictConns {
		ip, err := manet.ToIP(a)
		if err != nil {
			log.Tracef("Multiaddress has invalid ip: %v", err)
			return false
		}
		found := false
		for _, ipnet := range acceptedNets {
			if ipnet.Contains(ip) {
				found = true
				break
			}
		}
		return found
	}
	return !f.AddrBlocked(a)
}